Emergency radio beacons, especially those detectable by satellites, can be instrumental for search and rescue of people in distances, anywhere and anytime.
The use of satellites to detect and locate special-purpose radio beacons either manually activated or automatically activated upon aircraft crash or ship wreck, reduces the time required to alert the appropriate authorities and to accurately locate the distress site by the rescue team. The International Maritime Organization (IMO) and the International Civil Aviation Organization (ICAO) recommend that ships and aircraft carry Emergency Position Indicating Radio Beacons (EPIRBs) and Emergency Locator Transmitters (ELTs) respectively. Recently, small size Personal Locator Beacons (PLBs) are getting more and more popular for terrestrial use, by hikers, skiers, hunters, travelers, etc', as well as mariners and seafarers that might be in danger of Man Over Board (MOB) or other marine dangers.
A particular and important case of emergency radio beacons with a compatible constellation of satellites is the Cospas-Sarsat system. The current invention is particularly applicable to Cospas-Sarsat however reference to Cospas-Sarsat herein is intended to encompass any similar system, currently operating or to be deployed in the future.
Cospas-Sarsat is a satellite system designed to provide distress alert and location data to assist search and rescue (SAR) operations, using spacecraft and ground facilities to detect and locate the signals of distress radio beacons operating on 406 MHz (presently also 121.5 MHz however phasing out in a few years). The position of the distress and other related information is forwarded to the appropriate Search and Rescue Point of Contact (SPOC) through the Cospas-Sarsat Mission Control Center (MCC) network. The goal of the System is to support all organizations in the world with responsibility for SAR operations, whether at sea, in the air or on land.
The Cospas-Sarsat System provides distress alert and location to Rescue Coordination Centers (RCCs), for 406 MHz (and 121.5 MHz until 2009) radio beacons activated anywhere in the world. A detailed description of the Cospas-Sarsat System is provided in the document entitled “Introduction to the Cospas-Sarsat System, C/S G.003”—http://cospas-sarsat.org/Document/gDocs.htm.
Operational use of Cospas-Sarsat by SAR agencies started with the crash of a light aircraft in Canada, in which three people were rescued (Sep. 10, 1982). Since then, the System has been used for thousands of SAR events and has been instrumental in the rescue of over 20,000 lives worldwide.
The Cospas-Sarsat system is composed of:                Radio beacons which transmit distress or security alert signals        Instruments onboard satellites which detect the signals transmitted by distress radio beacons        Ground receiving stations, referred to as Local Users Terminals (LUTs), which receive and process the satellite downlink signal to generate distress alerts        Mission Control Centers (MCCs) which receive alerts produced by LUTs and forward them to Rescue Coordination Centers (RCCs), Search and Rescue Points Of Contacts (SPOCs) or other MCCs.        
Cospas-Sarsat provides alerting services for the following types of beacons:                Emergency Locator Transmitters (ELTs) for aviation use        Emergency Position-Indicating Radio Beacons (EPIRBs) for maritime use        Personal Locator Beacons (PLBs) for applications which are neither aviation nor maritime        
The Cospas-Sarsat satellite constellation is comprises of:                Low Earth Orbit (LOE) satellites        Geostationary (GEO) satellites        Medium Earth Orbit (MEO) satellites—in the near future—Galileo and GPS satellites will augment Cospas-Sarsat in order to provide a continuous, worldwide service. Galileo satellites will also provide a downlink signal to acknowledge the alarm transmission.        
Cospas-Sarsat determines the radio beacon's position either by measurement of RF Doppler shift (not applicable to GEOs) or by decoding the position data embedded in the beacon's message, in case that a navigation receiver (GPS, GLONASS, Galileo or similar) is comprised in the radio beacon.
Many radio beacons transmit, in addition to the standard 5 W 406 MHz alarm signal, an ancillary homing signal. This homing signal is usually low power (50-100 mW) and transmitted at 121.5 MHz or 243 MHz, which are aircraft emergency frequencies, reserved for emergency communications for aircraft in distress. 121.5 MHz is for civilian use, also known as International Air Distress (IAD) and 243 MHz is for military use, also known as Military Air Distress (MAD). Both are in use at the international level and are monitored by aircraft and ground stations worldwide.
Transmitting a 121.5 MHz homing signal would usually cause any aircraft flying nearby to render a siren sound on its radio speaker if set to the emergency channel.
When a SAR team approaches an activated radio beacon, it usually obtains the radio beacon's location information processed and delivered by Cospas-Sarsat. However, this information might not be updated due to communication problems from beacon to satellites or from shore stations to SAR team. Thus, homing signals can definitely assist SAR teams equipped with compatible Direction Finding (DF) devices.
However, determining direction and distance to such a homing signal has several drawbacks: a) direction and especially distance measurements are inaccurate; b) measurement is mostly sensitive to movements of the measuring device, almost impossible when done from a highly dynamic platform such as a vessel on high seas; c) operation range is limited due to the low transmission power of the homing signal; d) if a single 406 MHz antenna is used for the radio beacon, the homing RF signal might miss-match that antenna; e) a homing transmitter adds cost and weight and power consumption.
U.S. Pat. No. 6,992,623 and United States Patent Applications 20050073458 and 20040087284 to Street, suggest a 406 MHz emergency beacon with in-band homing transmitter, for example a 406 MHz homing transmitter (instead of 121.5 MHz). Since the beacon comprises also a standard 406 MHz satellite transmitter, the ancillary 406 MHz homing transmitter could share some electronic circuitry with the satellite transmitter and also enjoy good antenna matching. Still, other drawbacks of the current homing technique are not repaired.
U.S. Pat. Nos. 7,116,272 and 6,933,889 and United States Patent Application 20050270234 to Wolf et al disclose a system and method for a direction and distance finder for locating distress signals from a snow avalanche beacon. These inventions suggest a way to determine the distance to a distress radio beacon by measuring and analysing the beacon's RF path loss changes, in addition to RF direction finding. This method can be effective for very basic radio beacons and short distances, yet it obtains several drawbacks: direction measurement is done by manually pointing a device towards the radio beacon thus sensitive to movements and inaccurate; distance measurement requires advancing towards the beacon and is not accurate until significantly close to the radio beacon.
United States Patent Application 20060196499 to Cannizzaro discloses a scuba diver surface location, navigational and communication device and method. This invention, focused on positioning of divers on the water surface, is related to 2-D (two dimensions) positioning, i.e. distance and heading, and does not treat the 3-D problem, i.e. distance, direction (azimuth) and elevation (altitude). It is a local system for short range operation and does not deal with satellite communications. As such, it does not address specific issues related to satellite radio beacons. For example, in the Cospas-Sarsat system the entire 406-406.1 MHz band is divided into multiple narrowband discrete channels thus challenging a compatible receiver that should detect radio beacons transmitting spontaneously on different frequencies.
United States Patent Applications 20030003893 to Beni et al discloses a portable search and rescue system as quite known in the art. This system uses two ways (duplex or half duplex) portable radios embedded with GPS receivers and employs an interrogation protocol for location. It does not address satellite radio beacons which usually cannot be interrogated (since obtain an RF transmitter and no RF receiver), neither deals with other satellite radio beacon receiving issues such as the multiple Cospas-Sarsat channels.
Unfortunately, the standard 406 MHz radio beacon signal cannot be detected by standard aircraft receivers and it is neither on the maritime VHF band. Also, it is difficult to be tracked by regular DF devices since it is transmitted in bursts, about 0.5 seconds every 50 seconds. Yet, this signal could be very helpful as a homing signal for tracking radio beacons by SAR teams or vessels looking for a Man Over Board (MOB), for example, since it obtains high power and uses a very efficient radio frequency. Furthermore, this signal may contain very accurate location data which can yield to a fast and precise location of the radio beacon. As GPS and other navigation receivers get smaller and cheaper and power saver, manufacturers of emergency radio beacons embed such receivers in their products. A radio beacon integrated with a GPS receiver enables: a) precise location (meters instead of miles); b) compatibility with GEOs that can't perform Doppler measurements since don't move relatively to the earth.
Still, it is important to note that Cospas-Sarsat radio beacons operate on multiple discrete 3 KHz channels in the 406.0-406.1 MHz band. This spectrum is allocated by The International Telecommunication Union (ITU) for the dedicated use of low power satellite position-indicating radio beacons. Theoretically, a Cospas-Sarsat radio beacon can transmit on either one of the 33 (or 32) 3 KHz channels in this band, such as 406.022 MHz, 406.025 MHz, 406.028 MHz, etc'.
Practically, some frequencies in this band cannot be supported by the satellites' payloads; also Cospas-Sarsat regulates these channels according to capacity and load. Still, it would be desirable if a device designed to track satellite radio beacons would be able to detect all possible channels in the 406.0-406.1 MHz band. A wideband (100 KHz) receiver can do that however sensitivity would significantly be degraded as bandwidth gets wider so a narrower band receiver will probably achieve a longer detection range.
It is self evident that the time required to locate a distress and provide assistance has a direct impact on the probability of survival of the person in distress at sea or on land. According to Cospas-Sarsat, studies show that while the initial survivors of an aircraft crash have less than a 10% chance of survival if rescue is delayed beyond two days, the survival rate is over 60% if the rescue can be accomplished within eight hours. Similar urgency applies in maritime distress situations, particularly where injuries have occurred. Furthermore, accurate location of the distress can significantly reduce both SAR costs and the exposure of rescue forces to hazardous conditions, and clearly improve efficiency.
Therefore, it is quite clear that SAR operations could benefit from a device and method for precisely determining the direction and distance to a satellite radio beacon.
One particular example for the need of a device and method for precisely determining the direction and distance to a satellite radio beacon relates to Man Over Board (MOB) accidents. Thousands of persons are lost at sea every year due to MOB accidents. Detection and location of a person that falls from a vessel at sea is crucial since survival time in water is limited, typically 2-40 hours at 60-70° F. (16-21° C.) and 1-6 hours at 40-60° F. (4-16° C.). Mariners can carry satellite radio beacons such as small PLBs, possibly worn or inserted in a life vest, and alert Cospas-Sarsat upon a MOB event. However, in many cases, especially when MOB occurs far away offshore, the most and perhaps only reliable SAR can arrive from the very vessel from which MOB occurred. In such a case, a device for precisely determining the direction and distance to a satellite radio beacon which is attached to the MOB, such a device installed onboard, could be crucial.
The present art methods described above have not yet provided satisfactory solutions to the problem of precisely determining the direction and distance to a satellite radio beacon.
It is the object of the present invention to provide a device and method for precisely determining the direction and distance to a satellite radio beacon.
It is another object of the present invention to provide a device and method for precisely determining the direction and distance to a satellite radio beacon, by detecting and decoding the standard alarm message transmitted by radio beacons to Cospas-Sarsat satellites, in case that the message contains the radio beacon self position.
It is yet another object of this invention to provide a device and method for precisely determining the direction and distance to a satellite radio beacon, from relatively a long distance, by leveraging the high power and narrow bandwidth nature of the signal transmitted from radio beacons to satellites.
It is another object of this invention to provide a device and method for precisely determining the direction and distance to a satellite radio beacon, not sensitive to dynamic roll and pitch as often experienced on a vessel, by leveraging the Omni directional and digital nature of the signal and modulated information transmitted from radio beacons to satellites.
It is another object of this invention to provide a device and method for precisely determining the direction and distance to a satellite radio beacon, with minimal additional requirement from the radio beacon on weight, volume, power consumption and cost beyond what is required for precisely locating it by Cospas-Sarsat satellites.
It is yet another object of this invention to provide a device and method for precisely determining the direction and distance to a satellite radio beacon transmitting on any discrete channel in the allocated band.